Hit testing refers to a process that determines content that is located at a given set of coordinates in web content, such as a webpage. A common scenario for hit testing pertains to that which involves user input, e.g., receiving touch input or mouse click input. Specifically, in order to determine a correct response to user input, hit testing is performed to discover which content is the subject of the user's interaction. Anything that delays a hit test can, in turn, delay the system's response and degrade the user's experience.
In many systems, hit testing is performed on a main thread, for example, the user interface thread. The user interface thread can, however, frequently be busy performing other work. This other work can include execution of a script, for example JavaScript®, layout tasks, rendering operations, and the like. As a result, hit tests that occur on the main thread may be blocked for prolonged and variable periods of time.